Plenty bought it and plenty still run it: Gartner's July 2011 assessment of the global OS population suggested "Windows XP Home and Follow-Ons" had 68 million users, while XP Professional ran on 144 million machines.

A more recent Gartner study, the March 2012 Client OS and Office Survey reported 79% of business desktops and 45% of notebooks ran XP, based on responses from a 147-strong, self-selecting, group at its October 2011 US Symposium event. While the analyst firm notes that's not the most scientific of samples, the respondents represented organisations with a combined three million PCs in service.

Gartner's message to to those users is clear: flee migrate away from the OS ASAP, or as soon as is convenient before the end of its supported life on the date we note above.

Why is XP still with us?

The need for that warning, eleven years after XP's launch, seems odd. The specs of XP's launch version didn't hint at longevity. Processors with clock speeds of 233Mhz were supported, but you really needed 300Mhz to make XP sing. Disk drives greater than 137GB were frowned upon. USB 2.0 support only arrived with Service Pack 1 a year after launch.

Microsoft was nonetheless chuffed by XP’s slick new look and stability and felt sure the product would succeed. Your correspondent worked for a PR agency engaged by Microsoft Australia at the time of the launch, and one Redmondian colonist even suggested it would be a good idea to post a copy to every CIO in the land. The logic behind that idea was that XP's stability would prove that Microsoft's enterprise products were ready for the data centre and serious transactional applications.

That assertion seemed logical because XP was the first mainstream desktop OS Microsoft built on the Windows NT kernel**, which had rather more elegant plumbing than the Windows 9x family. But while XP was very usable it was a security mess, thanks in no small part to the decidedly leaky Internet Explorer 6.

XP nonetheless generated enormous sales and claimed colossal market share, although its tablet version was not a success.

Yet when Windows Vista came along with its unpleasant interface, XP’s modest virtues were thrown into flattering relief as users realised an upgrade to the latest version of Windows brought with it almost no tangible benefits. Netbooks then kept the OS relevant, as Microsoft realised the small machines’ underwhelming hardware would struggle to Vista.

XP, by then juiced up with a third service pack, therefore remained an option for new PCs into a tenth year.

Let the upgrade frenzy begin

Gartner believes 4% of PCs will still run XP beyond the end of its supported life, but plenty of migrations are afoot.

That's the case at Melbourne University, which has bitten the bullet and started to upgrade its desktops to Windows 7 after skipping Vista. The end of support is one motivator for the move.

But XP will live on in other places because apps written for or with it have become legacy software that users simply need to keep. A senior software engineer in a defence-oriented company, who cannot be identified for various reasons, told us that “our embedded systems use Serial-Link IP (SLIP) for remote comms and Windows 7 removed native support for SLIP, so we have a problem integration-testing our software on real hardware.”

“Things like unit tests rely on the old development environment,” he added. “So the most expedient way to do this is fire-up one of the old development PCs. We do plan to migrate the legacy code base to the new development environment (No more XP), but it's a low priority due to the rarity of occurrence.”

The OS will also continue to pop up in the virtual XP emulation mode available in the growing global fleet of Windows 7 machines. Yet support for XP will even disappear when used in that mode, leading Gartner to recommend that it “should be used sparingly and only for a limited time.”

“Relying too heavily on this method for application compatibility will add cost and management complexity, degrade performance, and delay the inevitable remediation of applications,” the firm warns in a document titled XP on Windows 7: Temporary Relief for Migration Headaches, but No Cure.

Even the virtual method keeping XP alive will vanish once Windows 8 appears in late 2012. While the new Windows will largely be Windows 7 beneath its Metro-fied skin, it appears XP mode will be omitted.

But XP won’t disappear entirely. It’s almost certainly fair to say that the XP-powered netbook acquired by your correspondent in mid-2010 is one of millions with a similar configuration. Many will still work by 2014. And by then XP may even be old enough to be have acquired a little retro chic. That won't protect the last few million users from the all-but-inevitable attacks criminals will unleash against the OS once the flow of patches ceases.

One last observation: while this story is published on Easter Sunday, 2012, Easter in 2014 falls on April 21st, 13 days after support ends. There'll be no XP resurrection. ®

*This story was filed from The Register's Australia bureau and timed to appear at 12:01 AM on the 8th of April, Sydney time. It may not be April 8th where you are just yet.

**We're not willing to classify Windows NT Workstation as a mainstream desktop OS.